124 
OTTO C. GLASER 
Change of diet 
Wright, Grosvenor and Cuenot, have studied the effect of an 
altered diet on the nematocyst content of eoUds, and have de- 
monstrated conclusively that the nettles vary with the food. 
Grosvenor's results particularly are so striking that there is 
scarcely need of insisting further on this point. I shall, how- 
ever, add one case out of a number which I have collected. 
In attempting to change the natural food of an eolid, one is 
confronted with an instance of strikingly specific diet, a con- 
dition suggested in nature. Montagua for instance, occurs only 
on Tubularia crocea, even when other hydroids are present. 
Indeed, late in the summer, when the colonies of T. crocea are 
degenerating or have almost disappeared, while Eudendrium is 
in fair condition, and Pennaria is flourishing, Montagua does not 
change its diet; instead it clings to its food supply as long as this 
endures, and in the end disappears to return onh^ with the next 
crop of the hydroid. 
This pronounced specificity interferes with attempts to replace 
the natural food of a species, but in a few instances I was able to 
substitute Aiptasia for Tubularia. The cerata of an eolid treated 
in this manner contained afterward the nematocysts character- 
istic of the anemone. A section through such a ceras is copied 
in fig. 4, and shows in addition to the great number of naturally 
captured nettles, those artificially introduced {A-F). 
Eolids devoid of nematocysts 
Grosvenor has cited Calma glaucoides as an eolid normally 
devoid of nematocysts. According to Hecht, C. glaucoides feeds 
on the eggs and embryos of Gotta and other fish. Whereas this 
species has neither nettles nor cnidophores, Calma cavolinii, the 
only other member of the genus, feeds on hydroids and has typical 
cnidophores crowded with nematocysts. 
These very suggestive facts can be duplicated within a given 
species. Thus in an earlier paper ('03), I mentioned an eohd 
which had been captured accidentally either before or during its 
